collector.java

package io.vertx.mysqlclient;

import io.vertx.sqlclient.Row;
import io.vertx.sqlclient.Tuple;

import java.util.function.BiConsumer;
import java.util.function.Function;

public class Main {

  static class Post {
    void addComment(Comment comment) {

    }
    void setAuthor(Author author) {

    }
  }

  static class Comment {
    void setAuthor(Author author) {

    }
  }

  static class Author {
  }

  public static void main(String[] args) {

    Builder<Author> b1 = Builder.mapOn("author", row -> {
      return new Author();
    });

    Builder<Comment> b = Builder.mapOn("commentId", row -> {
      return new Comment();
    }).combineWith(b1, Comment::setAuthor);

    Builder<Post> builder = Builder.mapOn("postId", row -> new Post())
      .combineWith(b, Post::addComment)
      .combineWith(b1, Post::setAuthor);

    //




  }

  interface Builder<T> {

    static <T> Builder<T> mapOn(String key, Function<Row, T> f) {
      throw new UnsupportedOperationException();
    }

    // Fluent
    <U> Builder<T> combineWith(Builder<U> builder, BiConsumer<T, U> foo);

  }

}